1. Field of the Invention
The current invention was developed in relation to the concept of an electronic fence transmitter with an adjustable transmitting or receiving distance which incorporates a fence wire, installed along a boundary of confinement. This confinement area is used to restrict a pet's activity, limiting it to being within the selected boundaries. A voltage is applied to the fence wire and is automatically changed accordingly with respects to the length of the fence wire. The emitted radio signals from the fence wire to the receiver can also be maintained at a constant level over the entire distance covered by the boundary.
2. Description of the Prior Art
In the past, this method has been used to confine a pet within a controllable boundary. A fence wire is installed surrounding the area in which a pet's activity can be confined and a signal is emitted from the fence wire. The receiver is attached to the pet that generates a shock when the pet approaches within a certain range of the fence wire.
An example of such a method in which a wire is installed for sending a signal is disclosed in U.S. Pat. No. 5,967,094. FIG. 1 illustrates the pet confinement system using a wire in accordance with the prior art.
A front yard or garden of a house ‘H’ has a confined area 2, in which a pet may move about freely. A loop of wire represented by a dashed line 3, is buried in the yard along the boundary of this confined area.
The loop of wire 3 is electrically connected to a transmitter 4a, is placed inside the garage ‘G’ of the house. This transmitter 4a generates RF boundary signals that are radiated through the buried loop of wire 3. As a pet approaches the wire within a predetermined range, a receiver 5a, attached to the pet 1, detects the boundary signal radiated from the wire 3.
When the receiver 5a receives the boundary signal radiated from the wire 3, a shock is applied to the pet 1 in order to prevent the pet from escaping from the confined area.
Furthermore, the transmitter 4a has a protective circuitry at the wire 3 that enables it to be protected from a surge of energy or shock, such as from lightening.
The transmitter, using the conventional fence wire installation method, adjusts the intensity of radio signals emitted from the fence wire. The receiver can receive a signal within a boundary width from the fence wire (ex. 5 meters inwards and 5 meters outwards from the fence wire). If the length of the fence wire is too long, the intensity of the radio signal is decreased due to a resistance in the fence wire. Therefore, the boundary should not be made too large or too small in order to accommodate the pet's activity, while having adequate strength and coverage of the emitting RF signals.
In other words, since the intensity of the signal that is applied to the fence wire from the transmitter has a continuously constant level, the intensity of the signal could be weakened by a resistance in the fence wire that is proportional to the length of the fence wire.
A resistance applied to the wire can be equivalent to a resistor R0, where this value is proportional to a length of the fence wire. For example, when a length of the fence wire using #18 AWG (America Wire Gauge) is 6,000 ft, the equivalent resistance is approximately 41.7Ω. When 4,000 ft of the same wire is used, the resistance becomes 27.8Ω, and finally when 2,000 ft is used, the resistance is approximately 13.9Ω.
Therefore, as the length of the fence wire increases, the area of the pet's activity can increase. However, the increase in the length increases the resistance in the fence wire and thus decreasing the intensity of the emitted radio signal to the intended receiver. The variation in receiving distance occurs at the boundary limits causing poor operation. This poses a problem that a pet's activity can't be controlled within this limited boundary.
FIG. 2 is a graph that depicts the distances for receiving a radio signal along the installed length of fence wire while the transmitter is applying a radio signal to the #18 AWG fence wire according to the prior art.
Herein, the dotted lines indicate the receiving distance from the inside of the fence wire and the solid lines represent the receiving distance from the outside of the fence wire. The bold, dotted and solid lines represent the receiving distances at each direction when a maximum voltage is applied to the fence wire while the fine dotted and solid lines are the receiving distances at each direction when a minimum voltage is applied to the fence wire.
As the conventional transmitter cannot automatically control the voltage applied to a fence wire, a voltage of 12V is applied to the fence wire up to 2,000 ft of an installation length. A voltage of 24V is applied to the fence wire above 2,000 ft of the installation length. The graph illustrates a result that measures a sensing distance for a radio signal emitted from a fence wire by the conventional receiver.
When an installation length of the fence wire is 4,000 ft, a pet approaches the fence wire within approximately 6 meters from an inward direction or an outward direction from the wire so that the receiver can receive a radio signal emitted from the fence wire. When this length of fence wire is 5,000 ft, the approaching distance is about 5 meters in each direction from the fence wire. When the installation length is 6,000 ft, the active distance range is about 4.3 meters in an inward direction or about 4 meters in an outward direction.
Illustrated in FIG. 3 above, is the conventional transmitter to solve this problem that the distance (or boundary width) for receiving a radio signal must vary according to an installation length of fence wire. Provided on the panel of the transmitter are an area selection switch 6, a wire connector 7, and a variable resistor 8. The variable resistor 8 can adjust the applied voltage according to the length of the fence wire. The area selection switch 6 can select a wide point or a narrow point according to an area of a restricted domain. The wire connector 7 can be connected with either thick or thin wire according to a length of the fence wire. The variable resistor 8 can adjust the applied voltage according to a length of the fence wire.
In the conventional transmitter, the area selection switch 6 can be controlled depending on a wide or a narrow area according to the area of the restricted domain so as to adjust the voltage applied to the fence wire. But, only two levels of the voltage can be selected (ex. high or low voltage), and it cannot overcome problems that the receiving boundary width has to be changed according to the length of the fence wire as shown in FIG. 2.
Also, both thick and thin wires are prepared, and the proper sized wire is connected to the wire connector 7 depending on the installation length of the fence wire. However, it also cannot overcome problems that the receiving boundary width has to be changed according to the length of the fence wire as shown in FIG. 2.
Furthermore, adjusting the variable resistor 8 can change the voltage applied to the fence wire. After adjusting the variable voltage, a user has to check along the fence wire with a hand-on receiver to confirm its operation. If the check is improper, the adjustment should be re-established, which can lead to problems.
As well, a user must learn a device control method for the transmitter to change an installation distance of the fence wire and a voltage to be applied to the fence wire, which poses a burden on a user.